The LookAt target location doesn't matter if it is z = 0 or z = 1000 or -1000?

[winterheat]

I am trying LookAt in OpenGL ES,

[FONT=Courier New][B]        gluLookAt(512, 384, 2000,
                  512, 384, 0,
                  0.0f, 1.0f, 0.0f);[/B][/FONT]

The second row is the Target's position... so I wonder, if I change the z from 0 to 1000 or -1000, shouldn't what is seen different? They turn out to be all the same, why is that?